There are many different applications for charge pump power converters such as e.g. for efficiently generating the supply rails for ground-centered class-G headphone drivers; these are a key feature customers expect in modern audio codecs. Magnetics-based power converters such as Buck converters are usually considered too costly and complex (inductor size and PCB space, on-chip flyback currents and voltage spikes, sensing and feedback control etc.) for this application.
There is still a need for improvements with present charge pumps such as:                A key requirement for any charge pump power converter is achieving low output impedance. This gives better load regulation, i.e. less output voltage droop and associated energy losses when load current is drawn from a given charge pump output.        In a specific case of a charge pump used to generate output stage supply voltages for a class-G amplifier, minimizing droop under load increases the overall amplifier efficiency by enabling closer envelope tracking (increasing efficiency is the main reason for using a class-G amplifier over a class-A or AB amplifier with fixed supply voltages).        A further desirable characteristic for a ground-centered charge pump when used to supply class-G amplifiers is equal output impedance on both outputs to give good output voltage symmetry under load, as the lowest of the positive or negative output voltage defines the peak voltage a sine wave can assume when being processed by the amplifier, and hence power deliverable to the amplifier load. FIG. 1 illustrates how the maximum signal 1 amplitude is set by the output with the most droop when loaded (POS is the positive charge pump output and NEG is the negative output).        
A special challenge for designers of charge pumps is:
1. Achieving high power conversion efficiency and, related,
2. Minimizing output impedance (to achieve good load regulation).